Vehicle antitheft systems have been provided that function by disabling a component in the ignition system of a vehicle unless a security code is transmitted to the system prior to starting the vehicle. An example of such a device is disclosed in U.S. Pat. No. 4,733,638 to Anderson, which discloses a transmitting device that can be manually operated to energize a relay within the casing of a vehicle starter motor. In turn, the relay, once energized, closes an auxiliary contact that is also located in the casing of the starter motor to thereby complete the electrical path from the vehicle's battery to a conventional starter solenoid. In accordance with well-known principles, when the ignition key is rotated to close the ignition switch, the starter solenoid both engages the Bendix gear of the starter with the vehicle flywheel, and closes a conventional starter switch to complete the electrical path between the battery and the starter motor to turn the Bendix gear and flywheel, thereby starting the vehicle.
Accordingly, the Anderson device, like many if not most such antitheft systems, does not directly control power to a starter motor, but rather indirectly controls power to the starter motor by controlling power to the starter solenoid. A principal reason why power to the solenoid is controlled is that the electrical current drawn by the solenoid is much less than the current drawn by the starter motor, thus permitting the use of relatively small, inexpensive auxiliary contacts by the antitheft systems.
In our above-referenced U.S. Pat. No. 5,564,376, we recognized that while somewhat effective, existing antitheft systems have certain drawbacks. For example, because many of its components are located within the casing of the starter motor, the Anderson device mentioned above cannot be easily integrated with existing starter motors. Further, from the above discussion it will be appreciated that the Anderson device is intended for use with ignition systems wherein the solenoid is housed with the starter motor. Indeed, the Anderson device cannot be used in conjunction with ignition systems wherein the solenoid is not co-housed with the starter motor.
In our prior patents we have also recognized that antitheft systems which can disable a starter solenoid that is housed apart from the starter motor can be, under certain circumstances, relatively easy to defeat because the solenoid is typically mounted in a location on the vehicle that relatively easy to access, compared to accessing the starter motor, and requires the jumpering of a relatively small amount of current, compared to the current that must be jumpered to defeat a circuit element in the main power line to the starter motor. For these reasons, we have provided a vehicle antitheft system which can be easily and quickly mounted in a comparatively inaccessible location, i.e., on the starter motor casing, which is difficult to defeat by jumpering, and which can be used in conjunction with existing stock starter motors.
Nevertheless, the present invention recognizes that some users desire solenoid disablement instead of starter motor power interrupt, because it is easier and less expensive to disable a solenoid as opposed to interrupting the main power to the starter motor. As understood herein, past solenoid-based security systems, such as that disclosed in PCT application no. WO 81/03002 to Blais, have drawbacks including the failure to recognize the importance of voltage regulation in antitheft systems that are powered by sources such as car batteries that do not always produce constant voltages. Accordingly, the present invention provides embodiments that address these considerations.